Basic calculations in Adobe Acrobat forms are coming out incorrect. How to fix this?

Just trying to calculate some basic addition, multiplying for tax, and adding the total. Something is causing my calculations to go haywire. 
Here's the custom code section:

// Retrieve the values of the fields

var ContractPrice = Number(this.getField("ContractPrice").valueAsString);

var BatteryPrice = Number(this.getField("BatteryPrice").valueAsString);

var OtherPrice = Number(this.getField("OtherPrice").valueAsString); // Assuming this could be 0 or any other value

// Calculate the sum of the prices var total = ContractPrice + BatteryPrice + OtherPrice;

// Calculate the total including tax by applying 6.75% var totalIncludingTax = total * (1 + 0.0675);

// Set the result to the current field, showing total price including tax event.value = totalIncludingTax.toFixed(2); // .toFixed(2) rounds the result to 2 decimal places